[RAC-3.0] Question 2-Way Binding Example?

[theladyjaye]

I'm assuming 2 way binding is something like this?

@IBOutlet weak var myNSTextField //...assume it's assigned
var myModelWithMutableProperties // ... assume it's assigned


let inputProducer = myNSTextField.rac_textSignal().toSignalProducer()

myModelWithMutableProperties.someName.producer.start(next: {value in
    self.myNSTextField.stringValue = value
})

inputProducer.start(next: { value in
    myModelWithMutableProperties.someName.value = value as? String
})

[neilpa]

I would take a look at ReactiveCocoa/EditableProperty that @jspahrsummers recently started to enable multi-way binding.

[larryonoff]

I assume that my code contains extra code, but I have implemented two-way binding for NSUserDefaults in the following way.

private let _property: MutableProperty<String>
var property: PropertyOf<String> {
    return PropertyOf(_property)
}

_property = MutableProperty<String>("")
_property <~ userDefaults.rac_signalForKey(SomeKey)

updatePropertyAction = Action<String, String, NoError> {
    userDefaults.setObject($0, forKey: UserDefaultsKeywordsKey)
    userDefaults.synchronize()

    return SignalProducer.empty
}

[theladyjaye]

how does updatePropertyAction get used? I don't see the connecting piece of code that makes use of that Action. everything else makes sense in your example.

[larryonoff]

The property and updatePropertyAction are implemented inside ViewModel. updatePropertyAction is triggered in ViewController. See

propertyTextView.rac_textSignal().toSignalProducer()
    |> ignoreError
    |> map { $0 as? String ?? "" }
    |> map { property in
        return self.viewModel.updatePropertyAction.apply(property) |> ignoreError
    }
    |> flatten(FlattenStrategy.Concat)
    |> start()

[larryonoff]

It would be great if @jspahrsummers comments about the direction of my thoughts.

[jspahrsummers]

@larryonoff Seems like that could cause a recursive notification if the thing observing the property is also the thing modifying user defaults.

[larryonoff]

@jspahrsummers I agree. This is why NSUserDefaults.rex_signalForKey was written in neilpa/Rex repo. Now it shouldn't cause a recursive notification.

extension NSUserDefaults {
    /// Sends value of key when the value is changed
    func rex_signalForKey(key: String) -> Signal<AnyObject?, NoError> {
        let (signal, observer) = Signal<AnyObject?, NoError>.pipe()

        // send initial value
        let initial: AnyObject? = self.objectForKey(key)
        sendNext(observer, initial)

        // observe other values
        let defaultsDidChange = NSNotificationCenter.defaultCenter().rac_notifications(name: NSUserDefaultsDidChangeNotification, object: self)
        defaultsDidChange.observe(next: { notification in
            let value: AnyObject? = self.objectForKey(key)

            sendNext(observer, value)
        }, completed: {
            sendCompleted(observer)
        })

        return signal
            |> skipRepeats { a, b in
                    if let a = a as? NSObject, b = b as? NSObject where a.isEqual(b) {
                        return true
                    } else {
                        return false
                    }
            }
    }
}

[jspahrsummers]

In any case, it looks like the question here has been answered.